An Eye on Aurora

Transorbital Endoscopic Image Guidance with Aurora

The area behind the eye is one of the last 'invisible' spaces in the body. The extreme delicacy of the eye makes accessing the region behind it very difficult. As a result, it remains one of the least-studied parts of the body and one of the most difficult to treat.

Direct access to the optic nerve has traditionally required an orbitotomy, an invasive procedure in which either the lateral boney wall of the orbit (eye socket) is removed (causing permanent facial scarring or disfigurement) or a rectus muscle is dissected from the side of the eyeball (and then later re-attached) allowing the eye to be carefully 'rotated' to expose the optic nerve. However, this process of moving the eye in the socket is technically difficult, and a number of things can go wrong that damage the eye.

The use of very small flexible endoscopes for orbital surgeries and orbital biopsies has been attempted, allowing access to the optic nerve and eliminating the need for an orbitotomy. But there are problems with navigation because the orbital structures are of similar colour, the traditional orbital landmarks are lost as the endoscope is moved through the orbit, and the orbital fat obscures the visualization of the optic nerve during the procedure.

Introducing image guidance to the transorbital endoscopic procedure may solve the problem of navigation, hopefully one day replacing the traditional operating room approach of the invasive and risk laden orbitotomy with a procedure room treatment application. The tiny sensor coil(s) of the Aurora system can be integrated into the endoscope to provide the necessary spatial tracking. A research project to study the feasibility of this idea is currently underway at Vanderbilt University.

If the endoscope is equipped with the proper cutting tools, a procedure known as optic nerve sheath fenestration could be performed. This procedure is sometimes indicated for patients diagnosed with pseudotumour cerebri, an excess of cerebrospinal fluid in the head, causing a swelling of the optic nerve and typically leading to intractable headaches and possible vision loss. In this procedure, the cutting tools would be used to create a tiny 'window' in the optic nerve sheath allowing cerebrospinal fluid to drain, thereby releasing pressure on the nerve and reducing swelling.

Optic neuropathies, a group of diseases characterized by visual loss due to optic nerve dysfunction, could also be treated with the endoscope. Optic neuropathies represent a leading cause of blindness and impaired vision, and the most common cause is glaucoma. A host of neuroprotective drugs have been shown to either decrease or prevent neuronal cell death when applied to the optic nerve. Current methods of ocular drug delivery such as topical administration of medications, transdermal therapeutic systems, transdermal injections, and intravitreal implants do not effectively get the drugs to the optic nerve axon. An endoscope tracked precisely and in real-time by the Aurora system and navigated by image guidance could deliver the drugs directly to the target site, providing a very effective treatment method for optic neuropathies.

References:

1. Atuegwu, Nkiruka C.; Galloway, Robert L., Jr. Ph.D.; Mawn, Louise A. M.D., "Transorbital Endoscopic Image Guidance', 29th IEEE EMBS Annual International Conference, paper SaP1C5.1, Lyon, France, August 23-26, 2007.
2. Salisbury, David F., "Free-electron laser used in human eye surgery for first time', Vanderbilt Register, October 9, 2000.

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